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A woman said to me, "You say one thing about nutrition. Other people say something else. It makes me just want to pull a towel over my head and forget about it all."

I hear you. Not everything important to know about nutrition can be explained in a sound bite or simplistic statement. And here's a great case in point:

We know that a diet rich in vegetables can lower blood pressure and improve heart function. But did we know that some of these health effects may be due to their high nitrate content?

Stop the presses. Aren't nitrates the substances used to cure meat products that we are supposed to avoid? Yes and no. Here is how it works, according to an excellent review article by registered dietitian and fitness expert Ellen Coleman.

Nitrate is found in all vegetables and is especially abundant in beetroot (aka "beets") and leafy greens such as spinach. Several clinical studies have found that supplementing the diet with about 2 cups daily of beetroot juice  rich in nitrates  not only lowered blood pressure but enhanced athletic performance by reducing the body's need for oxygen during exercise.

It makes sense. Dietary nitrate is converted in the body to nitrite which is then converted to nitric oxide. Nitric oxide is a "good guy" that regulates blood pressure and muscle function among other benefits. Thus, says Coleman, nitrate-rich foods are a source of beneficial nitric oxide that can potentially improve blood flow and enhance exercise capabilities.

Nitrate and nitrite salts such as sodium nitrate and potassium nitrite are also used to preserve food. And these levels are strictly controlled. And that's where the confusion begins.

Inorganic nitrate (what we find naturally in beets, spinach, celery and nitrate salts) is nontoxic at higher doses but inorganic nitrite (such as what might be found in a dietary supplement consumed by an overzealous athlete) can cause serious harm at considerably lower levels. In fact, nitrite toxicity can be lethal.

And here's another note of caution. "Organic" in the context of nitrate and nitrite are not what we are talking about in these dietary studies. "Organic" nitrate is found in the potent heart drug nitroglycerine, for example. "Any confusion that could lead to a large unintentional intake of organic nitrates or nitrites is potentially life threatening," warns Coleman.

That said, the "dose" of dietary nitrate (the amount found naturally in food) that was found to improve exercise performance and lower blood pressure in research studies was between 300 to 500 milligrams. This amount can be easily  and safely  found in foods. Two cups of beetroot juice, for example, contains about 500 milligrams of dietary nitrate. One-half cup of raw spinach contains 450 milligrams of nitrates. And a half cup of cooked collard greens contains 200 milligrams.

One harmless but sometimes alarming side effect of beet-eating: Pigments that make beets red can make urine that color, too. This too will pass and is not dangerous.

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